Evolution of the Circum-Kirsehir Block Foredeep Basins and Associated Post-Collisional Volcanic Rocks of Mid-Anatolia

Sener Usumezsoy

Anatolia, one of the most complex accretionary terrains in the Alpine-Himalayan range, is composed of the Kirsehir block and surrounding western Pontian, Menderes-western Tauride, eastern Pontian, and eastern Touride blocks. The main trunk of Anatolia was built up by the continental accretion of these blocks, which were jammed as a result of the convergence of Eurasia and Gondwanaland.

The circum-Kirsehir remnant foredeep basin resulted from the Neotethys irregular geometries of the Kirsehir block and surrounding accreted blocks. The Polath, Haymana, Tuz golu, and Ulukisla basins, located in the western Pontian belt, Kirsehir massif, and Menderes-Bolkar zone, were formed as a result of the obliteration of the Izmir-Ankara-circum-Kirsehir ocean by the continental accretion of these three blocks in the Paleocene. The Cankara-Corum basin, located between the eastern Pontian block and Kirsehir massif, the Sarkisla basin, situated between Kirsehir and the eastern Tauride platform, and the Susehri basin, extending between the eastern Pontian and Munzur carbonate platform of eastern Tauride, also developed from the Neotethys ocean by the obliteration of the Tokat Erzincan ceanic branches.

These basins were floored by the imbricated oceanic crust and bounded by the obducted oceanic crust and structural high of the subduction-associated accretionary prism of the Late Cretaceous. The sedimentary fill of this basin was derived mostly from either obducted oceanic crust or structural high subduction melange, and consisted of ophiolite-derived carbonate-cemented clastic beds and carbonates of the Paleocene or Eocene. The sedimentary beds in these basins are interlayered with alkaline volcanic and pyroclastic rocks, the product of the steeply dipping subduction of the cold dense oceanic floor of the remnant oceanic basin acquired from the Neotethys.

A great expanse of Paleocene-Eocene volcanic rock with alkaline tendencies that circumscribed the Kirsehir block are known as the Ulukisla volcanics in the Ulukisla basin, Kutudag volcanics in the Tuzgolu basin, Beynamaz volcanics in the Kargi belt, Cankiri volcanics in the Cankiri-Corum basins, Sarkisla volcanics in the Sarkisla basin. However, the Maden basin, located between the Keban-Malatya belt and Bitlis Poturge massif, is also constituted principally on the ophiolite and ensimatic island arc complex of the Late Cretaceous. The Thre modal tholeiitic calc-alkali and alkaline volcanic rocks of Eocene age filled in the Maden basin, a product of the combined processes of right lateral strike-slip events and a steeply dipping subduction remnant of the oceanic floor, which was trappe between the Bitlis-Poturge massif and Keban Malatya belt during the closure of the southern Branch (Guleman) of Neotethys.

The petrological characters of foredeep volcanics of the circum-Kirsehir reveal that these volcanics, interlayered with basin-fill clastic beds of the Paleocene and Eocene, are the product only of the upper mantle, without any continental-crust material. These accounts lead us to conclude that circum-Kirsehir basins were not floored by continental crust but were constructed above the oceanic crust.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.